In welding industry in recent years, there is an increasing demand for high-quality welding to improve productivity. It is particularly demanded to prevent spatters at arc start. It takes time to form a melt pool on the base material after an arc is started, and therefore, it takes time to stabilize the arc. For this reason, a lot of spatters are generated at arc start, and often adhere to the base material. In some cases, an additional process is required to remove adhered spatters, thereby decreasing welding productivity. In other cases, products are sold with spatters adhered to the base material without performing the additional process. This greatly impairs the product value.
According to the well-known conventional control of arc starting, the short-circuit welding control is switched to pulse welding control when a predetermined time has passed since short-circuit welding control was started at arc start (see, for example, Patent Literature 1).
FIG. 4 is a schematic configuration view of a conventional arc welding apparatus including input power supply 101, main transformer 102, primary rectifier device 103, switching element 104, reactor 105, and secondary rectifier device 106. Primary rectifier device 103 receives and rectifies the output of input power supply 101 and outputs the rectified result. Switching element 104 converts the DC output received from primary rectifier device 103 into an AC output so as to control a welding output. Main transformer 102 changes the voltage of the AC output received from switching element 104. The output of main transformer 102 is outputted as the welding output via secondary rectifier device 106 and reactor 105. Secondary rectifier device 106 rectifies the secondary output of main transformer 102.
The conventional arc welding apparatus further includes setting unit 135, which sets and outputs various parameters such as pulse current magnitude or pulse time. Setting unit 135 sets these parameters based on various setting conditions such as set current, set voltage, wire feed amount, the type of the shielding gas, the type of wire, the diameter of the wire, and welding method, which are entered through unillustrated input means. To set these parameters, setting unit 135 includes an unillustrated storage unit for storing a table or a formula to determine the parameters, and an unillustrated calculation unit.
The conventional arc welding apparatus further includes welding current detector 108, welding voltage detector 109, drive unit 134, short-circuit welding controller 136, pulse welding controller 137, and switching unit 138. Welding voltage detector 109 detects a welding voltage, and welding current detector 108 detects a welding current. Short-circuit welding controller 136 receives the outputs of welding current detector 108, welding voltage detector 109, and setting unit 135, and then outputs a command for performing short-circuit control.
As will be described later, short-circuit welding controller 136 performs short-circuit welding control in which short-circuiting and arcing are repeated for a predetermined time after the arc is started. Pulse welding controller 137 receives the outputs of welding current detector 108, welding voltage detector 109, and setting unit 135, and then outputs a command for performing pulse welding control. Short-circuit welding controller 136 and pulse welding controller 137 compares, for example, the output signals of welding current detector 108 and welding voltage detector 109 with parameter values (command values) received from setting unit 135. When the values of the output signals of welding current detector 108 and welding voltage detector 109 do not agree with the parameter values, short-circuit welding controller 136 and pulse welding controller 137 control the welding current and the welding voltage so that the values of the output signals agree with the parameter values.
Switching unit 138 receives the output of setting unit 135, and notifies drive unit 134 the timing to switch from short-circuit welding control to pulse welding control. Switching unit 138, which has a time-counting function, counts the time after the output of setting unit 135 is received and until a predetermined time elapses. Drive unit 134 receives the outputs of short-circuit welding controller 136, pulse welding controller 137, and switching unit 138. Drive unit 134 provides switching element 104 with either the output of short-circuit welding controller 136 or the output of pulse welding controller 137 according to the output of switching unit 138.
The following is a description of, with reference to FIGS. 4 and 5, a method for controlling arc starting by using the arc welding apparatus thus structured.
FIG. 5 shows an example of waveforms of a wire feed speed, a welding voltage and a welding current with time in consumable electrode arc welding. FIG. 6 shows the behavior of droplets formed in arc welding when the base material has a small melt pool. In the waveforms shown in FIG. 5, at a time T1, the start of welding is commanded. At a time T2, arc current is supplied and an arc is created to start short-circuit welding control. At a time T3, short-circuit welding control is switched to pulse welding control.
At the time T1 when the arc is created, drive unit 134 transmits the output of short-circuit welding controller 136 to switching element 104 based on the output of switching unit 138. Switching unit 138 counts the time elapsed since the time T2 when the welding current is detected. At the time T3 when the predetermined time elapses, drive unit 134 transmits the output of pulse welding controller 137 to switching element 104 so as to switch short-circuit welding control to pulse welding control.
From the time T2 when the arc is created until the time T3 when welding control is switched, short-circuit control is performed based on the output of short-circuit welding controller 136. When the time T3 is reached after the predetermined time has passed since time T2, switching unit 138 instructs drive unit 134 to switch welding control. At this moment, switching element 104 receives the output of pulse welding controller 137, and switches short-circuit welding control to pulse welding control. From the time T3 onward, pulse welding controller 137 performs pulse welding control.
Thus, according to the conventional method for controlling arc starting by using the arc welding apparatus, short-circuit welding control is performed after an arc starting current is supplied. This prevents arc interruption due to unstable arc when pulse welding control is started immediately after the arc starting current is supplied, and also prevents the generation and adhesion of spatters.
In the conventional arc welding apparatus, the short-circuit welding control is switched to pulse welding control when the predetermined time has passed since short-circuit welding control was started at arc start. This has reduced the generation of spatters at arc start.
As shown in FIG. 6, however, the melt pool formed during short-circuit welding immediately after an arc is started is much smaller than the melt pool formed during the subsequent pulse welding. Therefore, droplets formed immediately after pulse welding is started may spatter and adhere to the base material without being transferred to the melt pool. Thus, the conventional method can reduce the generation of spatters immediately after the arc is started, but cannot reduce the generation of spatters immediately after short-circuit welding control is switched to pulse welding control. As a result, large spatters may adhere to the base material.